DETROIT -- The 2012 Chevrolet Sonic sedan is more than a foot longer than its little brother, the Sonic hatchback.

But while General Motors' plan all along was to make the subcompact sedan a little longer for the sake of creating trunk space, the original intent was never to boost the length 14.1 inches beyond the five-door hatchback.

The result is a model with a spec that's nearly the same as the compact Chevrolet Cruze.

During the design process, "we felt very good about the balance of the hatch. As we put the sedan together at the same time, the sedan just felt from a proportional standpoint stubby. Proportionally it didn't feel right," says Ken Parkinson, executive director for GM design and Chevrolet brand champion.

"So we decided to add a little bit more on the rear length, pull the car together again and step back, and all of a sudden it felt really good. We knew proportionally that was the right thing to do."

Parkinson, interviewed this month at the Detroit auto show, said the plan all along was to make the sedan longer, but not a foot-plus.

"We wanted to have the appropriate amount of cargo space under the rear decklid. It was always going to be longer," he says.

The Sonic hatchback: GM designers were comfortable with its balance.

After the sedan's design was finished, the next step was getting approval for a longer car.

"We went through all the issues with engineering, manufacturing. Nothing was insurmountable. The car still met the targets that it needed to meet. The business case was good so it felt like the right thing to do," he says.

The result?

The subcompact Sonic sedan has good proportions and a trunk that is about the same size as the bigger Chevy Cruze.